The invention relates generally to concrete finishing devices and, more particularly, to truss screeds.
Truss screeds are widely used to level and preliminarily finish freshly poured concrete. A typical truss screed includes at least one screed plate and a triangular truss frame that supports the screed plate and other components of the machine. The ends of the screed plate are configured to be supported on an upper edge of a form surrounding a slab of freshly-poured concrete. In use, the screed is pulled along the form, either by a manually operated or power operated winch, so that the screed plate pushes the formed concrete ahead of it to level the concrete. Oftentimes, the screed is sectional. That is, it consists of modular sections that are connected to one another in an end-to-end fashion. Sections can be added or removed as desired to change the effective length of the screed, thus permitting the screed to be used on concrete slabs of variable widths. The relative angular orientation of the various sections can also be adjusted to alter the profile of the leveled concrete, e.g., to impart a crown or a slant to the leveled surface. Vibrational forces can be imparted to the screed plate during a concrete leveling operation. Vibration during screeding helps settle and densify the concrete. Vibrational screeding also removes air voids from the concrete and brings excess water and fine layers of concrete aggregated to the surface, hence partially finishing the leveled concrete. Vibrational forces are typically imparted using an exciter shaft that is located near the screed plate and that is driven to rotate via a motor such as an internal combustion engine. The exciter shaft supports eccentric weights that generate vibrations upon exciter shaft rotation. The vibrations are transmitted to the screed plate through the exciter shaft and its bearings.
A problem with traditional truss screeds is that the exciter shaft and associated bearings are not covered. They therefore are exposed to the wet concrete and, therefore, become soiled with concrete and debris. This soiling shortens the life of the bearings and other moving components of the screed.
To address these drawbacks, at least one proposal has been made to provide a shaft guard. However, the proposal proved unworkable because the shaft guard was complex and expensive. Additionally, the proposed shaft guard could not easily accommodate misalignment of the components during assembly thereof or flexing of the screed during angular adjustment of the screed sections for setting the profile of the leveled surface. It was also designed solely for use in a screed in which the exciter shaft is located well-above the screed plate. It also formed the uppermost structural element of the triangular truss frame.
Thus, there is a need to have a shaft guard that is easy to assembly, is relatively flexible, is self-retaining, and provides at least some sealing for the shaft. This need is particularly evident, yet particularly difficult to address, when the exciter shaft is located closely adjacent the concrete being leveled.
The invention, which is defined by the claims set out at the end of this disclosure, is intended to solve at least some of the problems noted above.
In accordance with a first aspect of the invention, a truss screed includes an improved shaft guard that is configured to cover the exciter shaft and eccentric weights of the screed""s exciter assembly. The shaft guard includes (1) tubing sections that surround the shaft and (2) joints that support the sections of tubing on the screed. The tubing may comprise simple plastic tubes formed from PVC or another suitable material. Each joint is sufficiently flexible and otherwise configured to accommodate component misalignment, facilitate assembly, and provide an at least quasi-seal.
In a first preferred embodiment of the shaft guard, the flexible joint includes a support cup and a spring ring made of a resilient material. The support cup supports the spring ring and the associated tubing section end on the bearing. The resilient spring ring is located axially between an end of the associated tubing section and an abutment surface on the support cup. The spring ring permits movement of the tubing section relative to the support cup while providing a seal against the ingress of dust, concrete, etc.
In a second embodiment of the shaft guard, each joint includes a bracket that fits over a bearing. The bearing and bracket are connected to the support cup via a cup.
Elongated slots may be provided in the base of the bracket and the bearing to provide flexibility and movement during assembly of the shaft guard components. Joints located at a juncture between adjacent screed sections also include a cup guide that bears the associated support cup while permitting limited tilting movement of the support cup relative to the bearing.
Hence, both types of joint accommodate component misalignment, provide an at least limited seal, and permit adjustment of the angular orientation of adjacent screed sections relative to one another.
These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.